Frequently Asked Questions about Primary, Medium, and High-Efficiency Air Filters in Cleanrooms
In the “primary efficiency + medium efficiency + high efficiency” three-stage filtration system of a cleanroom, filters of different levels often encounter various problems during operation due to differences in functional positioning and material properties. The following answers the core questions in combination with actual application scenarios.
In the “primary efficiency + medium efficiency + high efficiency” three-stage filtration system of a cleanroom, filters of different levels often encounter various problems during operation due to differences in functional positioning and material properties. The following answers the core questions in combination with actual application scenarios.
I. Issues related to selection and compatibility
1. How to determine whether the selection of primary, medium, and high-efficiency filters matches the requirements of the cleanroom?
The core of selection and matching lies in “gradient interception efficiency and system load adaptation”, which can be judged through three dimensions:
Clean level matching: High-efficiency filters directly determine the cleanliness level (for example, for ISO 5 grade, H13 or higher HEPA level is required). Medium-efficiency filters, as “transitional interception”, should correspond to F5-F9 grade (F7 can be selected for ISO 7-8 grade cleanrooms, and F9 is required for ISO 5-6 grade). Primary filters of G3-G4 grade can meet the pre-protection requirements.
Air volume matching: The rated air volume of each level of filter should be consistent with the system’s supply air volume, and a margin of 10% to 15% should be reserved. For instance, if the supply air volume of the clean room is 1000m³/h, the rated air volume of the selected filter should be ≥1100m³/h to prevent a sudden increase in resistance due to air volume overload.
Environmental adaptation: For high humidity (such as biological cleanrooms), waterproof filters (such as medium-efficiency waterproof non-woven fabric filter materials and high-efficiency stainless steel frames) should be selected. In environments with oil mist or chemical corrosion (such as semiconductor and chemical industries), anti-static and chemical-resistant filter materials (such as PTFE-coated high-efficiency filters) should be selected.
If “the resistance of the high-efficiency filter rises too fast”, “the cleanliness does not meet the standard”, or “the pre-filter gets clogged frequently”, it is very likely that the selection does not match the requirements.
2. Can primary and medium-efficiency filters replace high-efficiency filters or omit a certain stage of filtration?
It is absolutely irreplaceable, and all three stages of filtration are indispensable for the following reasons:
The essence of the efficiency difference: The primary filtration particle size is ≥5μm (intercepting dust and hair), the medium filtration particle size is ≥1μm (intercepting suspended particles), and the high filtration particle size is ≥0.3μm (intercepting sub-micron particles and microorganisms). There is an order of magnitude difference in filtration accuracy among the three. The primary and medium filtration cannot achieve the high filtration efficiency of the high filtration (for example, the high filtration efficiency of H13 grade is ≥99.97%).
System protection logic: If the primary and medium efficiency filters are omitted, large particles in the air will directly impact the high-efficiency filter materials (such as glass fiber, which is fragile), causing the high-efficiency filters to clog within 1-2 months (with a normal lifespan of 1-2 years), significantly increasing maintenance costs. If high-efficiency is used to replace medium-efficiency, it will fail rapidly due to excessive load, which is a case of “performance waste + cost waste”.
Ii. Operation and Fault issues
What are the reasons for the sudden increase or decrease in resistance during the operation of the filter?
Resistance is the core indicator reflecting the operating status of the filter. Abnormal changes need to be investigated immediately. The specific reasons are as follows:
| Abnormal resistance type | Possible causes (primary and intermediate effects) | Probable Cause (efficiency) |
| Suddenly increase |
1. A sudden increase in environmental dust content (such as external construction and equipment dust); 2. Dust accumulation and blockage at the seal between the filter and the frame; 3. Clogging of subsequent filters (such as medium-efficiency/high-efficiency filters) leads to an increase in system air pressure |
1. The pre-filter medium-efficiency filter failed, and a large amount of particles entered the high-efficiency filter. 2. Blockage of the supply air outlet in the clean room (such as incorrect closing of the air valve); 3. Local moisture and adhesion of high-efficiency filter materials (in high-humidity environments) |
| Suddenly decrease |
1. Filter material damage (such as tearing of primary non-woven fabric); 2. The installation clip of the filter has fallen off, creating a gap with the frame. 3. Air leakage in the air duct leads to insufficient air intake |
1.Filter material damage (such as impact during transportation/installation, or puncture due to excessively high wind speed); 2. Seal failure (such as drying up of the sealing liquid in the liquid tank or aging and breaking of the rubber strip); 3. Differential pressure gauge failure (The instrument needs to be calibrated first) |
2. If the integrity test (PAO test) of the high-efficiency filter fails, how should it be handled?
PAO testing is the core method for detecting leakage in high-efficiency filters (filter material damage, installation gaps). Non-conformities need to be dealt with step by step.
Locate the leakage point: Use an aerosol photometer to scan the “surface of the filter material, the frame, and the joint with the installation frame” of the filter to determine the leakage location (the leakage rate should be ≤0.01% to be qualified).
Targeted repair
If it is a small local damage to the filter material (≤5mm), a special PTFE repair film can be used for pasting (only 1-2 small damages are allowed, and the total area is ≤ 0.1% of the filter material area).
If the leakage occurs at the frame or the sealing area, the installation needs to be readjusted (such as replenishing the sealing liquid or replacing the aged rubber strip).
If the filter material is extensively damaged or still fails to meet the standards after repair, a new filter must be replaced immediately.
Re-inspection confirmation: After repair or replacement, PAO testing must be conducted again until it is qualified before it can be put into operation.
3. If the particle concentration in a cleanroom exceeds the standard, does it necessarily mean that there is a problem with the high-efficiency filter?
Not necessarily. The malfunction of the high-efficiency filter is one of the main reasons, but other factors need to be ruled out first. The troubleshooting logic is as follows:
Prioritize the inspection of high-efficiency filters: Test the resistance (whether abnormal) and integrity (whether leaking) of the high-efficiency filters in the corresponding area. These are the most direct influencing factors.
Check the pre-filter system: If the primary and medium-efficiency filters have not been replaced for a long time (such as more than 6 months), it will lead to “interception failure”, with a large number of particles entering the high-efficiency filter, indirectly causing the cleanliness to exceed the standard.
Rule out other system issues.
Insufficient air supply volume (fan failure, incorrect adjustment of the air valve) leads to a decline in purification capacity.
The pressure difference in the clean room is normal (insufficient positive pressure, backflow of external contamination).
Internal pollution sources include dust from production equipment and non-standard operation by personnel (such as not wearing clean suits).
It is recommended to check in the order of “high efficiency → medium efficiency/primary efficiency → system parameters → internal contamination” to avoid blind replacement of filters.
Iii. Maintenance and Lifespan Issues
How are the replacement cycles of primary, medium, and high-efficiency filters determined? Is there a fixed standard?
There is no absolute fixed standard for the replacement cycle. It should be comprehensively judged in combination with “resistance changes, cleanroom requirements, and environmental dust content”. The conventional reference is as follows:
PAO testing is the core method for detecting leakage in high-efficiency filters (filter material damage, installation gaps). Non-conformities need to be dealt with step by step.
Locate the leakage point: Use an aerosol photometer to scan the “surface of the filter material, the frame, and the joint with the installation frame” of the filter to determine the leakage location (the leakage rate should be ≤0.01% to be qualified).
Targeted repair
If it is a small local damage to the filter material (≤5mm), a special PTFE repair film can be used for pasting (only 1-2 small damages are allowed, and the total area is ≤ 0.1% of the filter material area).
If the leakage occurs at the frame or the sealing area, the installation needs to be readjusted (such as replenishing the sealing liquid or replacing the aged rubber strip).
If the filter material is extensively damaged or still fails to meet the standards after repair, a new filter must be replaced immediately.
Re-inspection confirmation: After repair or replacement, PAO testing must be conducted again until it is qualified before it can be put into operation.
3. If the particle concentration in a cleanroom exceeds the standard, does it necessarily mean that there is a problem with the high-efficiency filter?
Not necessarily. The malfunction of the high-efficiency filter is one of the main reasons, but other factors need to be ruled out first. The troubleshooting logic is as follows:
Prioritize the inspection of high-efficiency filters: Test the resistance (whether abnormal) and integrity (whether leaking) of the high-efficiency filters in the corresponding area. These are the most direct influencing factors.
Check the pre-filter system: If the primary and medium-efficiency filters have not been replaced for a long time (such as more than 6 months), it will lead to “interception failure”, with a large number of particles entering the high-efficiency filter, indirectly causing the cleanliness to exceed the standard.
Rule out other system issues.
Insufficient air supply volume (fan failure, incorrect adjustment of the air valve) leads to a decline in purification capacity.
The pressure difference in the clean room is normal (insufficient positive pressure, backflow of external contamination).
Internal pollution sources include dust from production equipment and non-standard operation by personnel (such as not wearing clean suits).
It is recommended to check in the order of “high efficiency → medium efficiency/primary efficiency → system parameters → internal contamination” to avoid blind replacement of filters.
Iii. Maintenance and Lifespan Issues
How are the replacement cycles of primary, medium, and high-efficiency filters determined? Is there a fixed standard?
There is no absolute fixed standard for the replacement cycle. It should be comprehensively judged in combination with “resistance changes, cleanroom requirements, and environmental dust content”. The conventional reference is as follows:
|
Filter level |
Core replacement basis | Regular replacement cycle (for ordinary cleanrooms) | Special circumstances adjustment |
|
Initial effect (G3-G4) |
The resistance reaches twice the initial resistance, or runs 1 to 3 times |
1 to 3 months | High dust content (such as in food processing) can be shortened to two weeks |
| Medium effect (F5-F9) | The resistance reaches 2 to 2.5 times the initial resistance, or it has been running for 3 to 6 months | Three to six months | The ISO Class 5 cleanroom needs to be equipped with F9 class, which can be shortened to 2-3 months |
|
High efficiency (H13-H14) |
The resistance reaches the final resistance (2.5 to 3 times the initial resistance), or the integrity test fails | One to two years | Biological cleanrooms and GMP pharmaceutical workshops must comply with regulatory requirements, with a maximum duration of no more than one year |
Key principle: Do not wait until the filter is completely clogged (the resistance far exceeds the final resistance) before replacing it; otherwise, it will cause the fan to overload, the air duct to vibrate, and even affect the stability of the pressure difference in the clean room.
2. What details should be noted when replacing the filter to avoid affecting the cleanroom environment?
The core of the replacement operation is “preventing secondary pollution + ensuring installation sealing”, and the following norms must be followed:
2. What details should be noted when replacing the filter to avoid affecting the cleanroom environment?
The core of the replacement operation is “preventing secondary pollution + ensuring installation sealing”, and the following norms must be followed:
Preparation stage: Select the “non-production period” of the clean room (such as night) for operation. Operators should wear full clean suits (hats, shoes, gloves, masks), clean the installation area (static pressure box, air outlet) in advance, and prepare new filters (integrity needs to be tested in advance).
Disassemble the old filter: When disassembling, seal the old filter with plastic film (especially in clean rooms containing contaminants, such as biological laboratories) to prevent dust on the filter material from scattering. At the same time, cover the opening of the static pressure box with a clean cloth to prevent dust from falling into the air duct.
Install a new filter.
Primary and medium efficiency: Align with the frame clips to ensure that the filter material has no wrinkles and the sealing rubber strips fit the frame without any gaps.
High efficiency: When using liquid tank sealing, ensure that the frame is fully immersed in the sealing liquid (depth ≥15mm); When sealing with rubber strips, tighten the pressure strip bolts evenly (with consistent torque) to avoid uneven local force distribution.
Post-replacement inspection: After the high-efficiency filter is installed, a PAO test must be conducted. For the primary and medium-efficiency filters, the operating resistance after installation should be detected. Only after confirming that there are no abnormalities should the system operation be resumed.
3. How to extend the service life of the filter and reduce maintenance costs?
The core logic is “reducing the load on the filter + optimizing the operating environment”. Specific measures:
Strengthened pre-filter protection: Regularly replace the primary and medium-efficiency filters (without delay) to ensure that the dust content in the air entering the high-efficiency filter is ≤0.1mg/m³, which can extend the service life of the high-efficiency filter by more than 50%.
Control the dust content in the environment: Set up air showers and changing rooms at the entrance of the clean room to reduce the dust brought in by personnel. The production equipment should be cleaned regularly to prevent dust from rising inside.
Stable operating parameters: Keep the system air volume, temperature, and humidity (10-30℃, 40%-65%), and pressure difference (5-10Pa) within the design range to prevent sudden increases in filter load due to parameter fluctuations.
Establish file traceability: Record the “installation date, initial resistance, maintenance record” of each filter, predict the replacement time through data, and avoid replacing too early or too late.
Iv. Other high-frequency issues
What is the difference between the “rated air volume” and the “designed air volume” of a filter?
Rated air volume: The “optimal operating air volume” marked on the filter at the factory is the air volume value at which the filter can achieve the rated efficiency and maintain stable resistance (determined by the manufacturer through testing).
Design air volume: The “actual supply air volume of the system” is calculated based on the area of the cleanroom, floor height, and air change rate (for example, if the air change rate of an ISO Class 5 cleanroom is ≥240 times /h, the design air volume is calculated accordingly).
When selecting the type, it is necessary to ensure that the design air volume is ≤ the rated air volume × (1+15% margin), which not only avoids overload but also reserves the space for system fluctuations.
2. What are the differences between the filters in biological cleanrooms and those in ordinary industrial cleanrooms?
Biological cleanrooms need to pay additional attention to “microbial interception and anti-spread”. The differences in filters mainly lie in three points:
High-efficiency filter media: H14 grade (efficiency ≥99.995%) is preferred. In some scenarios, “antibacterial-coated filter media” should be selected to inhibit the growth of microorganisms on the surface of the filter media.
Frame and seal: A stainless steel frame (waterproof and anti-corrosion) must be used, and a liquid groove seal should be adopted for sealing (to prevent microorganisms from penetrating through the gaps).
Disposal: The spent filters after replacement must first undergo moist heat sterilization (121℃ for 30 minutes) or chemical sterilization, and then be sealed and disposed of as hazardous waste to prevent microbial leakage.
Disassemble the old filter: When disassembling, seal the old filter with plastic film (especially in clean rooms containing contaminants, such as biological laboratories) to prevent dust on the filter material from scattering. At the same time, cover the opening of the static pressure box with a clean cloth to prevent dust from falling into the air duct.
Install a new filter.
Primary and medium efficiency: Align with the frame clips to ensure that the filter material has no wrinkles and the sealing rubber strips fit the frame without any gaps.
High efficiency: When using liquid tank sealing, ensure that the frame is fully immersed in the sealing liquid (depth ≥15mm); When sealing with rubber strips, tighten the pressure strip bolts evenly (with consistent torque) to avoid uneven local force distribution.
Post-replacement inspection: After the high-efficiency filter is installed, a PAO test must be conducted. For the primary and medium-efficiency filters, the operating resistance after installation should be detected. Only after confirming that there are no abnormalities should the system operation be resumed.
3. How to extend the service life of the filter and reduce maintenance costs?
The core logic is “reducing the load on the filter + optimizing the operating environment”. Specific measures:
Strengthened pre-filter protection: Regularly replace the primary and medium-efficiency filters (without delay) to ensure that the dust content in the air entering the high-efficiency filter is ≤0.1mg/m³, which can extend the service life of the high-efficiency filter by more than 50%.
Control the dust content in the environment: Set up air showers and changing rooms at the entrance of the clean room to reduce the dust brought in by personnel. The production equipment should be cleaned regularly to prevent dust from rising inside.
Stable operating parameters: Keep the system air volume, temperature, and humidity (10-30℃, 40%-65%), and pressure difference (5-10Pa) within the design range to prevent sudden increases in filter load due to parameter fluctuations.
Establish file traceability: Record the “installation date, initial resistance, maintenance record” of each filter, predict the replacement time through data, and avoid replacing too early or too late.
Iv. Other high-frequency issues
What is the difference between the “rated air volume” and the “designed air volume” of a filter?
Rated air volume: The “optimal operating air volume” marked on the filter at the factory is the air volume value at which the filter can achieve the rated efficiency and maintain stable resistance (determined by the manufacturer through testing).
Design air volume: The “actual supply air volume of the system” is calculated based on the area of the cleanroom, floor height, and air change rate (for example, if the air change rate of an ISO Class 5 cleanroom is ≥240 times /h, the design air volume is calculated accordingly).
When selecting the type, it is necessary to ensure that the design air volume is ≤ the rated air volume × (1+15% margin), which not only avoids overload but also reserves the space for system fluctuations.
2. What are the differences between the filters in biological cleanrooms and those in ordinary industrial cleanrooms?
Biological cleanrooms need to pay additional attention to “microbial interception and anti-spread”. The differences in filters mainly lie in three points:
High-efficiency filter media: H14 grade (efficiency ≥99.995%) is preferred. In some scenarios, “antibacterial-coated filter media” should be selected to inhibit the growth of microorganisms on the surface of the filter media.
Frame and seal: A stainless steel frame (waterproof and anti-corrosion) must be used, and a liquid groove seal should be adopted for sealing (to prevent microorganisms from penetrating through the gaps).
Disposal: The spent filters after replacement must first undergo moist heat sterilization (121℃ for 30 minutes) or chemical sterilization, and then be sealed and disposed of as hazardous waste to prevent microbial leakage.
